'use strict';

var Validator = require('./Validator');

/**
 * The guy responsible for template loading.
 *
 * Provide the actual templates via the `config.elementTemplates`.
 *
 * That configuration can either be an array of template
 * descriptors or a node style callback to retrieve
 * the templates asynchronously.
 *
 * @param {Array<TemplateDescriptor>|Function} loadTemplates
 * @param {EventBus} eventBus
 * @param {ElementTemplates} elementTemplates
 */
function ElementTemplatesLoader(loadTemplates, eventBus, elementTemplates) {
    this._loadTemplates = loadTemplates;
    this._eventBus = eventBus;
    this._elementTemplates = elementTemplates;

    var self = this;

    eventBus.on('diagram.init', function () {
        self.reload();
    });
}

module.exports = ElementTemplatesLoader;

ElementTemplatesLoader.$inject = [
    'config.elementTemplates',
    'eventBus',
    'elementTemplates'
];


ElementTemplatesLoader.prototype.reload = function () {

    var self = this;

    var loadTemplates = this._loadTemplates;

    // no templates specified
    if (typeof loadTemplates === 'undefined') {
        return;
    }

    // template loader function specified
    if (typeof loadTemplates === 'function') {

        return loadTemplates(function (err, templates) {

            if (err) {
                return self.templateErrors([err]);
            }

            self.setTemplates(templates);
        });
    }

    // templates array specified
    if (loadTemplates.length) {
        return this.setTemplates(loadTemplates);
    }

};

ElementTemplatesLoader.prototype.setTemplates = function (templates) {

    var elementTemplates = this._elementTemplates;

    var validator = new Validator().addAll(templates);

    var errors = validator.getErrors(),
        validTemplates = validator.getValidTemplates();

    elementTemplates.set(validTemplates);

    if (errors.length) {
        this.templateErrors(errors);
    }

    this.templatesChanged();
};

ElementTemplatesLoader.prototype.templatesChanged = function () {
    this._eventBus.fire('elementTemplates.changed');
};

ElementTemplatesLoader.prototype.templateErrors = function (errors) {
    this._eventBus.fire('elementTemplates.errors', {
        errors: errors
    });
};